The following Patents describing automatic tuning devices use electromechanical devices to change or maintain pitch.
US Patent Application 20080006140, Adams, Jan. 10, 2008 “Device and Method for Automatic Tuning of a String Instrument in Particular a Guitar” discloses an automatic tuning devise for a guitar, by recording a tone and output of a corresponding digital signal to a comparator device for comparison of the digital signal with a digital signal corresponding to the desired tone, then adjust the tension of the string accordingly.
US Patent Application 20070240554, Hany, Oct. 18, 2007, “Musical tuning switcher” discloses that the invention is an attachable string tension control device for adjusting the pitch of each string of a musical instrument. Allowing an operator to switch instantly between a variety of pre-selected tunings.
US Patent Application 20070214935, Lyles, Sep. 20, 2007, “Stringed musical instrument using spring tension” discloses a stringed musical instrument employs springs to apply tension to corresponding musical strings. Each spring is chosen and configured for its ability to impart a string tension generally matched to the appropriate tension of the string at perfect tune.
US Patent Application 20060037459, Skinn, Feb. 23, 2006 “Apparatus and method for self-tuning stringed musical instruments with an accompanying vibrato mechanism” discloses that an automatic tuning guitar system for a stringed instrument is provided having a string adjustment assembly comprising a motor and gear assembly.
U.S. Pat. No. 6,278,047, Cumberland, Aug. 21, 2001 “Apparatus for tuning stringed instruments” discloses a microprocessor-controlled tuning apparatus for a stringed instrument, wherein the tension of a string is detected by a sensor, compared with a reference value, and readjusted until the detected value conforms with the reference value.
U.S. Pat. No. 5,886,270, Wynn, Mar. 23, 1999 “An electromechanical tuner for stringed instruments” discloses that the invention is an automatic tuning guitar system for a stringed instrument. An input sensor detects the tone of a plucked string and converts it to a square wave of the detected frequency, which is compared by the microprocessor and energizes the solenoid for engaging the gear mechanism for tightening or loosening the string to obtain the required frequency.
U.S. Pat. No. 5,859,378 Freeland, Jan. 12, 1999 “Musical instrument self-tuning system with cape mode” discloses a control system for automatically tuning a stringed musical instrument with a capo installed.
U.S. Pat. No. 5,824,929, Freeland, Oct. 20, 1998 “Musical instrument self-tuning system with calibration library” discloses a control system for automatically utilizing a library of calibration functions to tune a stringed musical instrument in a plurality of operating conditions without recalibration.
U.S. Pat. No. 6,437,226 Oudshoorn, et al. (2002)
U.S. Pat. No. 6,184,452 Long (2001)
U.S. Pat. No. 5,886,270 Wynn (1999)
U.S. Pat. No. 5,824,929 Freeland, et al. (1998)
U.S. Pat. No. 5,767,429 Milano, et al. (1998)
U.S. Pat. No. 5,528,970 Zacaroli (1996)
U.S. Pat. No. 5,343,793 Pattie (1994)
U.S. Pat. No. 5,095,797 Zacaroli (1992)
U.S. Pat. No. 4,958,550 Kugimoto (1990)
U.S. Pat. No. 4,803,908 Skinn, et al. (1989)
U.S. Pat. No. 4,584,923 Minnick (1986)
U.S. Pat. No. 4,228,715 Nourney (1980)
U.S. Pat. No. 4,088,052 Hedrick (1978)
These systems or devises are all need to be added on a musical instrument or modify the musical instrument and no one use optical pickup to tune a stringed musical instrument.